虽然做出来了，但是感觉写得不够简洁

C++

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
    if(!p&&!q) return true;
    if(!p||!q) return false;
    if(p->val==q->val) 
    {
        if(!p->left&&!q->left&&!p->right&&!q->right)
        return true;
        if(p->left&&q->left||p->right&&q->right)
        {
            return isSameTree(p->left,q->left)&&isSameTree(p->right,q->right);
        }
        else 
        {
            return false;
        }
    }
    return false;  
    }
};

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
    if(p==null&&q==null) return true;
    if(p==null||q==null) return false;
    if(p.val==q.val) 
    {
        if(p.left==null&&q.left==null&&p.right==null&&q.right==null)
        return true;
        if(p.left!=null&&q.left!=null||p.right!=null&&q.right!=null)
        {
            return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right);
        }
        else 
        {
            return false;
        }
    }
    return false;
    }
}

Javascript

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {boolean}
 */
var isSameTree = function(p, q) {
    if(p===null&&q===null) return true;
    if(p===null||q===null) return false;
    if(p.val===q.val) 
    {
        if(!p.left&&!q.left&&!p.right&&!q.right)
        return true;
        if(p.left&&q.left||p.right&&q.right)
        {
            return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right);
        }
        else 
        {
            return false;
        }
    }
    return false;
};

最优解

C++,和我思路一样，但是写的很简洁，要学习

class Solution {
public:
    bool isSameTree(TreeNode *p, TreeNode *q) {
    if (p == NULL || q == NULL) return (p == q);
    return (p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right));
    }
};

Java，思路同上

public boolean isSameTree(TreeNode p, TreeNode q) {
    if(p == null && q == null) return true;
    if(p == null || q == null) return false;
    if(p.val == q.val)
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    return false;
}

代码实际做了两件事，判断节点是否存在，判断节点值是否相同